Method of producing beraprost

ABSTRACT

An improved method is described for making single isomers of synthetic benzoprostacyclin analog compounds, in particular the pharmacologically active 314-d isomer of beraprost. In contrast to the prior art, the method is stereoselective and requires fewer steps than the known methods for making these compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/440,418, filed Feb. 23, 2017, which is a Continuation of U.S.application Ser. No. 15/094,081, filed Apr. 8, 2016, which is aDivisional of U.S. application Ser. No. 14/645,715, filed Mar. 12, 2015,which is a Divisional of U.S. application Ser. No. 14/294,384, filedJun. 3, 2014, which is a Divisional of U.S. application Ser. No.13/524,568, filed Jun. 15, 2012, now U.S. Pat. No. 8,779,170, whichissued on Jul. 15, 2014, which claims priority from U.S. ProvisionalApplication No. 61/497,754, filed Jun. 16, 2011, the entirety of whichis incorporated herein by reference.

FIELD

The present application relates to a process for selectively producingsingle-isomer benzoprostacyclin derivatives including beraprost and itsderivatives.

The present invention also relates to a novel process for attaching thealpha side-chain to single-isomer key intermediate leading to beraprostand related derivatives.

BACKGROUND OF THE INVENTION

Prostacyclin derivatives are useful pharmaceutical compounds possessingactivities such as platelet aggregation inhibition, gastric secretionreduction, lesion inhibition, and bronchodilation. Beraprost is asynthetic benzoprostacyclin analogue of natural prostacyclin that iscurrently under clinical trials for the treatment of pulmonaryhypertension and vascular disease (excluding renal disease) in NorthAmerica and Europe.

Beraprost and related benzoprostacyclin analogues of the formula (I) aredisclosed in U.S. Pat. No. 5,202,447 and Tetrahedron Lett. 31, 4493(1990). Furthermore, as described in U.S. Pat. No. 7,345,181, severalsynthetic methods are known to produce benzoprostacyclin analogues.

Known synthetic methods generally require one or more resolutions ofintermediates to obtain the pharmacologically active isomer of beraprostor a related benzoprostacyclin analogue. Also, current pharmaceuticalformulations of beraprost or a related benzoprostacyclin analogues mayconsist of several isomers of the pharmaceutical compound, and only oneof which is primarily responsible for the pharmacologic activity of thedrug. Isolation of the pharmaceutically active isomer of beraprostcompounds from current synthetic methods requires multiple preparativeHPLC or chromatographic purification procedures or multiplerecrystallizations that are not amenable to a commercially applicablescale. Therefore, it is desired to achieve an efficient, commerciallyapplicable synthetic route to the active isomer of beraprost or arelated benzoprostacyclin analogue.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method which canproduce the pharmaceutical compound represented by the general formula(I) in a substantially isomerically pure form, in fewer steps than theprior art and in commercially useful quantities. Another object of thepresent invention is to provide a method which can produce the tricyclicintermediates represented by the general formula (IV) and (V) in asubstantially isomerically pure form which can be used for theproduction of pharmaceutical compounds represented by the generalformula (I) or other similar compounds. Yet another object of thecurrent invention is to provide a novel method which can attach thealpha side-chain to single-isomer key intermediate leading to thepharmaceutical compound represented by the general formula (I). Thisinvention also claims the preparation of compound (VII) where 6, 2a=H,also referred to as the diol single-isomer exclusively in 95-100%purity, which can be transformed into beraprost and related derivativesof the general formula (I).

One embodiment provides for a process for preparing a compound of thefollowing formula:

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl, comprising the steps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups, with a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene of formula (IV) to form the aromatic    product of the following formula:

-   (3) Reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane to form a compound of the following    formula:

-   (5) selectively deprotecting the primary hydroxyl protective group,    followed by oxidation of the primary hydroxyl group to the    corresponding aldehyde, followed by coupling with a side-chain of    the formula:

wherein R⁴ and R⁵ are each defined above to form a compound of thefollowing formula:

-   (6) reduction of the ketone, deprotection of any remaining hydroxy    protective group and optionally converting the R^(1a) into a cation    or H to form a compound of the following formula:

In another embodiment, the compound of formula (I) is produced as asubstantially pure single isomer. In another embodiment, R¹ is a cationor H, R² and R³ are H, R⁴ and R⁵ are CH₃. In another embodiment, R², R³,R^(2a) and R⁶ each independently represent trimethylsilyl,triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl,phenyldimethylsilyl, or tetrahydropyranyl. In another embodiment, thecycloaddition of step (1) is an inverse electron demand Diels Alderreaction followed by thermal decarboxylation. In another embodiment, thearomatization step (2) is treatment of the compound of formula (IV) withpalladium on carbon.

Another embodiment provides for a process of for preparing thestereoselectively produced isomeric compound of the following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups and R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl comprising the steps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups to form a compound of the following formula:

wherein R^(2a), R⁶ and R⁷ are each defined above;

-   (2) aromatization of the cyclodiene of formula (IV) to form the    aromatic product of the following formula:

wherein R^(2a), R⁶ and R⁷ are each defined above. In one embodiment,R^(2a) and R⁶ each independently represent trimethylsilyl,triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl,phenyldimethylsilyl, or tetrahydropyranyl. In another embodiment, thecycloaddition of step (1) is an inverse electron demand Diels Alderreaction followed by thermal decarboxylation. In another embodiment, thearomatization step (2) is treatment of the compound of formula (IV) withpalladium on carbon. Another embodiment provides a process for preparinga compound of the following formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl, comprising thesteps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups, with a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene of formula (IV) to form the aromatic    product of the following formula:

-   (3) Reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane followed by deprotection of the hydroxyl    protective groups to form a compound of the following formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl. In anotherembodiment, the compound of formula (VII) is produced as a substantiallypure single isomer.

Another embodiment provides for compounds represented by the formula:

wherein x is

R⁴ represents H or C₁₋₃ alkyl, and

-   R⁵ represents H or C₁₋₆ alkyl, and the compound has a chiral purity    of at least 95%. Additional embodiments provide a chiral purity of    at least 95%, 97%, 99%, or greater than 99%. Another embodiment    provides R⁴ and R⁵ are each CH₃.

Another embodiment provides for a process for preparing a substantiallypure compound of the following formula:

wherein

-   R² represents H or a hydroxy protective group,-   R⁴ represents H or C₁₋₃ alkyl,-   R⁵ represents H or C₁₋₆ alkyl, and-   Z represents C₁₋₁₂ alkyl-COOR¹², R¹² is a cation, H, or C₁₋₁₂ alkyl,    comprising the steps of:-   (1) reacting an aldehyde of the formula

with a substantially pure compound of the formula:

wherein Z′ is C₁₋₁₂ alkyl-COOR^(12′), R^(12′) is a C₁₋₆ alkyl or aprotecting group, R^(2a) is a hydroxy protecting group, R⁴ and R⁵ areeach defined above to form a compound of the following formula:

-   (2) selectively reducing the carbonyl and deprotecting secondary    alcohol to form a substantially pure compound of the following    formula:

and

-   (3) optionally deprotecting the ester of protected acid of Z′ to    form an acid or salt thereof. In one embodiment, the selective    reduction of the carbonyl includes an asymmetric catalyst.

In one embodiment, the step 3 is not optional, and Z′ is C₁₋₁₂alkyl-COOR^(12′), and R^(12′) is a C₁₋₆ alkyl. In one embodiment, thestep 3 is not optional, and R⁴ and R⁵ are each CH₃, Z is (CH₂)₃COOR¹²and R¹² is a cation or H. In one embodiment, R¹² is a cation and thecation is K⁺. In one embodiment, the resulting substantially purecompound comprises greater than 99% of the isomer represented by thefollowing formula:

DESCRIPTION OF THE FIGURES

FIG. 1 shows an embodiment of the synthesis of the side chain compoundfor coupling to the core beraprost analogue.

FIG. 2 shows Beraprost 314d and its isomers

FIG. 3 shows an embodiment of selective protection strategy leading toan enone intermediate

FIG. 4 shows an embodiment of the asymmetric synthesis of Beraprost froman enone intermediate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

All references cited herein are incorporated by reference in theirentirety.

Various inventions and/or their embodiments disclosed herein relate tomethods of synthesizing a substantially pure isomer of beraprost or itsrelated derivatives. In one preferred embodiment, the substantially pureisomer of beraprost is represented by the formula (I). In anotherpreferred embodiment, the substantially pure isomer of beraprost isBeraprost (314d) or a related analogue, such as a salt, solvate orprodrug thereof. Other embodiments include compounds that are novelintermediates of one or more of the synthetic routes disclosed herein.

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl.

Unless otherwise specified, “a” or “an” means “one or more” throughoutthis specification and claims.

The term “or” as used herein means “and/or” unless specified other wise.

Important synthetic methods which can be used as appropriate herein toprepare compounds are generally known in the art and are described in,for example, March's Advanced Organic Chemistry, 6^(th) Ed., 2007; T. W.Greene, Protective Groups in Organic Synthesis, John Wiley and Sons,1991.

When referring to a moiety (e.g. a compound) in singular, the plural ismeant to be included. Thus, when referring to a specific moiety, e.g.“compound”, this means “at least one” of that moiety, e.g. “at least onecompound”, unless specified otherwise.

As used herein, “halo” or “halogen” or even “halide” can refer tofluoro, chloro, bromo, and iodo.

As used herein, “alkyl” can refer to a straight-chain, branched, orcyclic saturated hydrocarbon group. Examples of alkyl groups includemethyl (Me), ethyl (Et), propyl (e.g., n-propyl and iso-propyl), butyl(e.g., n-butyl, iso-butyl, sec-butyl, tert-butyl), pentyl groups (e.g.,n-pentyl, iso-pentyl, neopentyl), and the like. In various embodiments,an alkyl group can have 1 to 30 carbon atoms, for example, 1-20 carbonatoms (i.e., C₁-C₂₀ alkyl group). In some embodiments, an alkyl groupcan have 1 to 6 carbon atoms, and can be referred to as a “lower alkylgroup.” Examples of lower alkyl groups include methyl, ethyl, propyl(e.g., n-propyl and iso-propyl), and butyl groups (e.g., n-butyl,iso-butyl, sec-butyl, tert-butyl). In some embodiments, alkyl groups canbe substituted as defined herein. In some embodiments, substituted,saturated hydrocarbons, C1-C6 mono- and di- and pre-halogen substitutedsaturated hydrocarbons and amino-substituted hydrocarbons are preferred,with perfluromethyl, perchloromethyl, perfluoro-tert-butyl, andperchloro-tert-butyl being the most preferred. The term “substitutedalkyl” means any unbranched or branched, substituted saturatedhydrocarbon, with unbranched C1-C6 alkyl secondary amines, substitutedC1-C6 secondary alkyl amines, and unbranched C1-C6 alkyl tertiary aminesbeing within the definition of “substituted alkyl,” but not preferred.In some embodiments, the term “alkyl” means any unbranched or branched,substituted saturated hydrocarbon. In some embodiments, cycliccompounds, both cyclic hydrocarbons and cyclic compounds havingheteroatoms, are within the meaning of “alkyl.” In some embodiments,“haloalkyl” can refer to an alkyl group having one or more halogensubstituents, and can be within the meaning of “alkyl.” At variousembodiments, a haloalkyl group can have 1 to 20 carbon atoms, forexample, 1 to 10 carbon atoms (i.e., C₁-C₁₀ haloalkyl group). Examplesof haloalkyl groups include CF₃, C₂F₅, CHF₂, CH₂F, CCl₃, CHCl₂, CH₂Cl,C₂Cl₅, and the like. Perhaloalkyl groups, i.e., alkyl groups where allof the hydrogen atoms are replaced with halogen atoms (e.g.,perfluoroalkyl groups such as CF₃ and C₂F₅), are included within thedefinition of “haloalkyl.” In some embodiments, “alkoxy” can refer to—O-alkyl group, and can be within the meaning of “alkyl.”. Examples ofalkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy(e.g., n-propoxy and isopropoxy), t-butoxy groups, and the like. Thealkyl group in the —O-alkyl group can be substituted with 1-5 R¹ groupsand R¹ is as defined herein.

As used herein, “hydroxy protective group” refers to the generallyunderstood definition of an alcohol or hydroxy protecting group asdefined in T. W. Greene, Protective Groups in Organic Synthesis, JohnWiley and Sons, 1991 (hereinafter “Greene, Protective Groups in OrganicSynthesis”).

As used herein, “protecting group” is used as known in the art and asdemonstrated in Greene, Protective Groups in Organic Synthesis.

As used herein, substantially pure compound or isomer refers to oneisomer being 90% of the resulting isomeric mixture, or preferably 95% ofthe resulting isomeric mixture, or more preferably 98% of the resultingisomeric mixture, or even more preferably 99% of the resulting isomericmixture, and most preferably above 99% of the resulting isomericmixture.

One aspect of the invention is a synthetic method for synthesizingBeraprost (314d) or a related analogue, such as a salt, solvate orprodrug thereof from a Corey Lactone, such as a compound represented byFormula (II)

In one embodiment, the present invention relates to a method for makinga substantially pure isomer of beraprost or its related derivatives ofthe following formula (I):

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl, comprising:

-   (1) performing a cycloaddition reaction between a compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups or H, and a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl, and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene compound of formula (IV) to form the    aromatic product of the following formula:

-   (3) reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane to form a compound of the following    formula:

-   (5) selectively deprotecting the primary hydroxyl protective group,    followed by oxidation of the primary hydroxyl group to the    corresponding aldehyde, followed by coupling with a side-chain of    the formula:

wherein R⁴ and R⁵ are each defined above and (VIII) is substantially asingle isomer to form a compound of the following formula:

-   (6) reduction of the ketone, deprotection of any remaining hydroxy    protective group and optionally converting the R^(1a) into a cation    or H to form a compound of the following formula:

In the present invention, the single pharmacologically active isomer ofberaprost corresponds to the 314-d isomer of beraprost or itscorresponding salt or other pharmaceutically useful related derivative,such as for example, prodrug or solvate. This 314-d isomer compound isrepresented by the compound of formula (I) wherein wherein R¹ is acation or H, R² and R³ are H, R⁴ and R⁵ are CH₃.

In one embodiment, R^(2a) and R⁶ independently represent hydroxyprotecting groups and are different protecting groups. In oneembodiment, R^(2a) is a silyl protecting group, such as for example,trimethylsilyl, triethylsilyl, t-butyldimethylsilyl,t-butyldiphenylsilyl, phenyldimethylsilyl. Additional silyl protectinggroups are recited in Greene, Protective Groups in Organic Synthesis,and are incorporated by reference. In one embodiment, R⁶ is a protectinggroup that is capable of protecting a primary alcohol without reactingwith a secondary alcohol, such as for example a trityl group. AdditionalR⁶ protecting groups meeting this requirement may be found in Greene,Protective Groups in Organic Synthesis, and are incorporated byreference.

In one embodiment, the cycloaddition of step (1) may be achieved with aninverse electron demand Diels Alder reaction followed by thermaldecarboxylation to form endo and exo isomers. The subsequentaromatization to compound (V) eliminates said isomers. In oneembodiment, aromatization may be achieved by dehydrogenation, forexample, palladium on carbon may be utilized to convert the diene ofcompound (IV) into the aromatic moiety of compound (V).

The reduction of the ketone in step (6) may be achieved using anon-selective reducing agent, such as for example, sodium borohydridewith cerium trichloride heptahydrate, and the subsequent diastereomersseparated, or alternatively a chiral reducing agent capable ofselectively reducing the ketone may be used to obtain substantially oneisomer of the resulting alcohol. Selective reducing agents are known inthe art and include, for example: (R)-(+)-2-Butyl-CBS-oxazaborolidineand catecholborane, (R)-(+)-2-Methyl-CBS-oxazaborolidine andcatecholborane, (+) DIP-chloride, NaBH₄ and2-(3-Nitrophenyl)-1,3,2-dioxaborolane-4S,5S-dicarboxylic acid(D-TarB-NO₂), modified DIBAL reagents, and modified LAH agents.

In one embodiment, the compound of formula (I) is produced as the singleisomer represented by formula (I) and in substantially isomerically pureform. In one embodiment, the product represented by formula (I)comprises 90% of the resulting isomeric mixture, or preferably 95% ofthe resulting isomeric mixture, or more preferably 98% of the resultingisomeric mixture, or even more preferably 99% of the resulting isomericmixture, and most preferably above 99% of the resulting isomericmixture.

In another embodiment of this invention is a method comprising steps (1)through (4) followed by deprotection of any alcohol protection groups toyield compound of formula (VII) wherein R^(2a) and R⁶ are H and R^(1a)is methoxy. This compound is isolated as substantially one isomerrepresented by the compound of formula (VII).

Another aspect of the present invention provides a novel method that canattach the alpha side-chain to single-isomer key intermediate leading tothe pharmaceutical compound represented by the general formula (I). Thenovel process provides for producing the four-carbon alpha side-chain ofberaprost or its related derivatives from the core intermediate ester ofthe compound of formula (V) comprising conversion of the compound offormula (V) to a benzyl alcohol of formula (X) followed by oxidation ofbenzyl alcohol to an aldehyde of formula (XII) followed by addition of acarbon to said aldehyde to form an alkyne compound of formula (VI). Oneskilled in the art would appreciate that extension of the alphaside-chain may proceed from the benzyl alcohol of formula (X) byconversion of the alcohol to a leaving group such as R¹⁰ of the formula(XI) followed by nucleophilic displacement. Furthermore, a Wittig orsimilar type reaction may be used to couple a side chain to the benzylaldehyde of formula (XII).

In another embodiment, analogues of the single-isomer key intermediatemay include an alpha side-chain of more than four carbons. For exampleScheme 1 demonstrates that the benzyl alcohol of formula (X) can beconverted to the compound of formula (XI) followed by nucleophilicdisplacement resulting in (XIII). In another embodiment, the aldehyde offormula (XII) may be subjected to a Wittig-type reaction to produce acompound of formula (XIII). In a further embodiment, the aldehyde offormula (VI) may be converted to a compound of formula (XIII) by methodsknown in the art or analogous to methods disclosed herein.

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups and R¹⁰ to R¹² are defined above, and may be optionallysubstituted with one or more functional groups. A compound of formula(XIII) can be subjected to steps (5) and (6) to produce additionalberaprost analogues.

Another aspect of this invention relates the side-chain coupling andvariations on said side-chain. The trans-alkene of beraprost and itsderivatives is achieved through Wadworth-Emmons-type reaction. Theside-chain is produced as substantially a single isomer. Synthesis ofthe side-chain coupling product of the formula (VIII) may be achievedfrom a single isomer Weinreb amide compound of the following formula:

wherein R⁴ and R⁵ are each defined above.

Furthermore, the compound of formula (XIV) may be synthesized accordingto reagents known in the art from a compound of the formula (XV) bydeprotonation and subsequent selective addition to an compound with asuitable leaving group, such as for example compound (XVI).

resulting in the compound:

The compound of formula (XVII) may be converted to a compound of formula(XIV) by methods known in the art. Compound (XIV) may subsequently beconverted in to a compound of the formula (VIII) by methods analogous tothose disclosed herein.

Furthermore, another embodiment of this invention includes manipulationof the side chain coupling product as shown in Scheme 2. Variation ofthe side-chain allows additional analogues of beraprost to be explored.In one embodiment, the compound of the formula (XV) may be reacted witha compound of the formula (XVIII), wherein R¹³ is C₁₋₁₂ allyl, C₁₋₁₂alkene, C₁₋₁₂ alkyne, C₁₋₁₂ cyclo alkyl, C₁₋₁₂ cyclo alkene, or C₁₋₁₂cyclo alkyne, and further manipulated by methods analogous to thosedisclosed herein or known in the art to form a Weinreb amide of formula(XIX). The methods for these reactions are analogous to those for theproduction of compound (XIV) or are known in the art. A compound of theformula (XIX) may then be converted into a coupling product suitable forWadworth-Emmons-type coupling analogous to compound of formula (VIII).The resulting coupling product may be coupled with a compound suitablefor Wadworth-Emmons-type coupling disclosed herein, for example acompound of the formula (VII) that has been selectively deprotected atthe primary hydroxyl protective group, followed by oxidation of theprimary hydroxyl group to the corresponding aldehyde.

wherein R⁴ and R¹³ are previously defined. In one embodiment, X is H. Inanother embodiment, X is Ph. Additional moieties, such as analogues ofPh and other aryl, heteroaryl or alkyl moieties may also serve as X. Inone embodiment, the phosphonate product is produced with chiral purityof 97 percent or more, or 99 percent or more.

Additional embodiments include side-chain compounds represented by thestructures

wherein R⁴, R⁵ and R¹³ are previously defined and the chiral purity is97 percent or more, or 99 percent or more. A preferred embodimentincludes compounds represented by the structures

wherein the chiral purity is 97 percent or more, or 99 percent or more.

Side-chain compounds may be produced by the methods described herein,including the exemplary methods shown in FIG. 1

The present invention is further illustrated by, though in no waylimited to, the following examples.

Example 1: Synthetic Route to the Single Isomer of a Compound of Formula(I)

Preparation of (2)

A 1-L, three-necked, round-bottomed flask equipped with a mechanicalstirrer, a dropping funnel, a thermocouple and an argon inlet-outletadapter connected to a bubbler was charged with Corey lactone (1) (10g), anhydrous dichloromethane (100 mL), and 2,6-lutidine (27 mL) underargon. A solution of t-butyldimethyl trifluoromethane sulfonate (37.4mL) in dichloromethane (50 mL) was added to the reaction mixturedrop-wise, while keeping the temperature between −10° C. to −20° C. overa period of 20-40 minutes. After complete addition, the reaction mixturewas allowed to warm-up to ambient temperature. After 2-4 h, the progressof the reaction was monitored by thin-layer chromatography. Aftercompletion of the reaction, the reaction mixture was concentrated invacuo to obtain a crude product. The crude product was chased with MTBEto remove dichloromethane completely. The crude product was dissolved inMTBE (100-150 mL) and washed with water (1×100 mL), saturated sodiumbicarbonate (1×100 mL), brine (1×150 mL), dried over anhydrous sodiumsulfate (10 g), and filtered. The filtrate was evaporated in vacuo to aafford crude, viscous liquid (30.4 g). The crude product was purified bycolumn chromatography using 230-400 mesh silica gel. A solvent gradientof ethyl acetate in hexanes (2-12%) was used to elute the product fromthe column. All fractions containing the desired product were combinedand concentrated in vacuo to give pure product (2) as a white solid(20.8 g, 89.4%).

Preparation of (3)

A 1-L, two-necked, round-bottomed flask equipped with a mechanicalstirrer, a dropping funnel, a thermocouple and an argon inlet-outletadapter connected to a bubbler was charged with intermediate 2 (20.0 g),and toluene (200 mL). The temperature of the reaction mixture wasmaintained at −50° C. to −70° C. under nitrogen using dry-ice-acetonebath. While maintaining the temperature of the reaction mixture at −50°C. to −70° C., diisobutylaluminium hydride (DIBAL, 60 mL, 1.0M intoluene) was added drop wise during 20-30 minutes. The progress of thereaction was monitored by TLC. The reaction mixture was quenched withmethanol (10 mL) at −20° C., water (300 mL), followed by addition ofdiluted hydrochloric acid (˜20%). The organic layer was separated andaqueous layer was extracted with MTBE (2×100 mL). The combined organiclayers were washed with saturated sodium bicarbonate (1×150 mL), brine(1×150 mL) and, dried over sodium sulfate (10 g). The organic layer wasfiltered. The filtrate was concentrated in vacuo, to give a yellow,viscous oil (20.4 g). The crude product was used as such in the nextstep.

Preparation of (4)

A 1-L, three-necked, round-bottomed flask equipped with a mechanicalstirrer, a thermocouple, and an argon inlet-outlet trap was charged withlactol intermediate 3 (20 g), anhydrous dichloromethane (200-250 mL),triethylamine (69.2 mL), and dimethylamino pyridine (DMAP, 0.6 g). Thetemperature of the reaction mixture was reduced to −20° C. A solution ofmethanesulfonyl chloride (7.7 mL) was added drop wise under argon whilekeeping the temperature around −20° C. After complete addition, theprogress of the reaction was monitored by TLC. The temperature of thereaction mixture was allowed to warm-up to ambient temperature. Thereaction mixture was heated to reflux for 2-4 h. The reaction mixturewas concentrated in vacuo to obtain crude product. The crude product waspurified by column chromatography using 230-400 mesh silica gel andeluted with a gradient solvent of ethyl acetate in hexanes (0-10%). Thefractions containing the desired product were combined and evaporated invacuo to afford intermediate 4 (as a viscous liquid, 11 g).

Preparation of (6)

A 1-L, two-necked, round-bottomed flask equipped with a mechanicalstirrer, and an argon inlet-outlet trap was charged with a solution ofintermediate (4, 10.0 g), dichloroethane (DCE, 100-150 mL), compound 5(2.6 g), and Eu(hfc)₃ (1.4 g) at room temperature under argon. Thereaction mixture was stirred and heated to reflux for 1.0 h and theprogress of the reaction was monitored by TLC in order to ensure thatstarting material 5 has been consumed completely. After 1.0 h, thetemperature of the reaction was reduced below reflux temperature andcompound 5 (1.0 g) was added to the reaction mixture. The temperature ofthe reaction was increased to reflux. In a similar manner, after half anhour, compound 5 (0.9 g) was added and the reaction was continuouslyrefluxed again. When the TLC of the reaction mixture indicated almostcomplete consumption of intermediate 4, the solvent was evaporated undervacuum to give a residual viscous liquid. The brown, viscous liquid waschased with toluene and dissolved in toluene (100-150 mL). The reactionmixture was heated to reflux again for 6-8 h. The progress of thereaction was monitored by TLC. After completion of the reaction, it wasconcentrated in vacuo to obtain the crude product 6 as a viscous oil.The crude product was purified by column chromatography using 230-400mesh silica gel and eluted with a gradient solvent of ethyl acetate inhexanes (4-40%). The fractions containing the desired product werecombined and concentrated in-vacuo to yield the intermediate 6, as acolorless, viscous oil (9.87 g, 77%).

Preparation of (7)

A 500-mL, one-necked, round-bottomed flask equipped with a magneticstirrer, an argon inlet-outlet trap, and a condenser was charged with asolution of intermediate 6 (7.6 g) in toluene (70-100 mL) under argon.At room temperature, palladium on carbon (1.52 g, 5%, 50% wet) wascharged, and the reaction mixture was heated to reflux for 8-12 h. Thereaction mixture was allowed to cool to room temperature, and thereaction mixture was filtered through a pad of Celite. The filtrate wasconcentrated in-vacuo to yield crude product 7, as a viscous liquid. Thecrude product 7 was purified by column chromatography using 230-400 meshsilica gel. A solvent gradient of ethyl acetate in hexanes (0-15%) wasused to elute the product from the column. The fractions containing thedesired product were evaporated in-vacuo to yield pure key intermediate(7) as viscous liquid (4.0 g, 43%).

Preparation of (8)

A 500-mL, three-necked, round-bottomed flask equipped with a magneticstirrer, and an argon inlet-outlet trap, and a thermocouple was chargedwith a solution of intermediate 7 (3.90 g) in toluene (40-60 mL,anhydrous). The reaction mixture was cooled to −25° C. to −50° C., anddiisobutylaluminium hydride solution (DIBAL, 16.60 mL, 1.0M in toluene)was added drop-wise, while keeping the temperature of the reactionmixture between −25° C. to −50° C. The reaction mixture was stirred for1-2 h. The progress of the reaction was monitored by TLC. The reactionmixture was quenched with methanol (2-4 mL), followed by acidificationwith dilute hydrochloric acid (20%, 50 mL). The organic layer wasseparated and aqueous layer was extracted with MTBE (2×50 mL). Thecombined organic layers were washed with saturated sodium bicarbonate(1×50 mL), brine (1×50 mL), and dried over sodium sulfate (10 g). Theorganic layer was filtered. The filtrate was concentrated in vacuo, togive a viscous oil (8, 3.73 g).

The crude product 8 was used as such in next step.

Preparation of (9)

A 500-mL, one-necked, round-bottomed flask equipped with a magneticstirrer was charged with a solution of intermediate 8 in dichloromethane(40-70 mL), and manganese dioxide (8.30 g) under nitrogen. The reactionmixture was stirred vigorously at ambient temperature over night. Theprogress of the reaction was monitored by TLC. The reaction mixture wasfiltered through a pad of Celite and the filtrate was concentratedin-vacuo to obtain the crude product 9 as colorless, viscous liquid oil(3.4 g, 92%). In this case the crude product was used as such in thenext step (as the TLC indicated pure material). The crude product 9 mayoptionally be purified by column chromatography.

Preparation of (10)

A 50-mL, one-necked, round-bottomed flask equipped with a magneticstirrer, and an argon inlet-outlet trap was charged with a solution ofintermediate 9 (260 mg) in methanol (5-10 mL), potassium carbonate (232mg), and dimethyl(1-diazo-2-oxopropyl)phosphonate (215 mg) at roomtemperature under argon. The mixture was stirred at ambient temperatureover night. After ˜16 h, the progress of the reaction was monitored byTLC. The solvent was evaporated in vacuo and dissolved in MTBE (10-15mL). The organic layer was washed with brine (1×10 mL), dried overanhydrous sodium sulfate, filtered, and the filtrate concentrated invacuo to obtain crude product 10, as a viscous oil.

Preparation of (11)

A 50-mL, one-necked, round-bottomed flask equipped with a magneticstirrer, and an argon inlet-outlet trap was charged with a solution ofintermediate 10 (55 mg) in acetonitrile (5-10 mL), and copper iodide (3mg) at room temperature under nitrogen. To the stirred solution, ethyldiazoacetate (14 mg dissolved in 1.0 mL of acetonitrile) was added. Thereaction mixture was stirred overnight. The progress of the reaction wasmonitored by TLC. The reaction mixture was concentrated in-vacuo to givethe crude product 11. The crude product was purified by columnchromatography using 230-400 mesh silica gel and the column was elutedwith a gradient solvent of ethyl acetate in hexanes (0-10%). Thefractions containing the desired compound were evaporated in vacuo toyield intermediate 11, as a colorless, viscous oil (38 mg, 60%).

Preparation of (12)

A 50-mL, three-necked, round-bottomed flask equipped with magneticstirrer was charged with a solution of intermediate 11 (50 mg) inanhydrous acetonitrile (5-10 mL) and palladium on carbon (10 mg, 5%, wet50%). The reaction mixture was stirred and air was removed by vacuum.The vacuum in the flask was replaced by hydrogen from an attachedballoon. The process was repeated 5-10 times. Finally, the reactionmixture was stirred at room temperature under hydrogen overnight. Theprogress of the reaction was monitored by TLC. After completion of thereaction, the reaction mixture was filtered through a pad of Celite andthe filtrate concentrated in-vacuo to give the crude product 12. Thecrude product 12 was purified by flash column chromatography using230-400 mesh silica gel. A solvent gradient of ethyl acetate in hexanes(2-8%) was used to elute the product from the column. The fractionscontaining the desired product 12 were combined and evaporated in-vacuoto yield product 12, 41 mg (˜80%).

Preparation of (13)

A 25-mL, one-neck, round-bottomed flask equipped with a magnetic stirrerwas charged with intermediate 12 in a solution of acetic acid:THF:water(1.0:3.0:0.5). The reaction mixture was stirred at ambient temperatureovernight. The progress of the reaction was monitored by TLC. Afterapproximately 90% completion of the reaction (by TLC), the reactionmixture was concentrated in-vacuo to give a residual viscous liquid. Thecrude product was dissolved in ethyl acetate (10 mL) and organic layerwas washed with saturated sodium bicarbonate solution (1×10 mL), brine(1×10 mL), dried over anhydrous sodium sulfate (1.0 g), filtered and thefiltrate evaporated in-vacuo. The crude product 13 was purified bycolumn chromatography using 230-400 mesh silica gel. A solvent gradientof ethyl acetate in hexanes (4-100%) was used to elute the products fromthe column. The fractions containing the desired product 13 werecombined and evaporated in-vacuo to yield a viscous liquid of pureproduct 13, (120 mg). The purification of crude product by column alsogave starting material 12 (36 mg), diol product (52 mg).

Preparation of (14)

A 100-mL, one-neck, round-bottomed flask equipped with a magneticstirrer, an argon inlet-outlet trap was charged with a solution ofintermediate 13 (160 mg) in dichloromethane (5-10 mL). To the stirredsolution, add Dess-Martin reagent (233 mg) at ambient temperature undernitrogen. The reaction mixture was stirred for 0.5-1.0 h. The progressof the reaction was monitored by TLC. The reaction mixture was quenchedwith NaHCO₃ (solid powder, 500 mg). The product 14 was purified bycolumn chromatography using 230-400 mesh silica gel by loading thereaction mixture directly on the column, and the column was eluted withdichloromethane (100%). The fractions containing the desired product 14were evaporated in-vacuo to yield pure product 14 (125 mg, 73%).

Preparation of (15)

A 50-mL, three-neck, round-bottomed flask equipped with a magneticstirrer and an argon inlet-outlet trap was charged with the phosphonateside-chain (57 mg), THF (5 mL), and sodium hydride (9.0 mg). The mixturewas stirred at 0-10° C. for 15-20 minutes under nitrogen. Theintermediate 14 (85 mg, dissolved in 5 mL of THF) was added drop-wiseduring a period of 5-10 minutes. The reaction mixture was stirred 2-3 h.The temperature of the reaction mixture was allowed to rise to ambienttemperature. The progress of the reaction was monitored by TLC after 2-3h. The reaction mixture was quenched with acetic acid (couple of drops)and the reaction mixture was extracted with MTBE (3×10 mL). The combinedorganic layers were washed with saturated sodium bicarbonate (1×10 mL),brine (1×10 mL), dried over anhydrous sodium sulfate, filtered, andevaporated in-vacuo to give a crude product. The crude product 15 waspurified by column chromatography using 230-400 mesh silica gel, thecolumn was eluted with gradient of ethyl acetate and hexanes (5-12%).The pure fractions containing the desired compound 15 were combined andevaporated in-vacuo to yield pure product 15 as a viscous liquid (72 mg,70%).

Preparation of (16)

A 50-mL, one-neck, round-bottomed flask equipped with a magneticstirrer, was charged with a solution of intermediate 15 in methanol andcerium chloride heptahydrate (CeCl₃.7H₂O, 28 mg). To the reactionmixture, sodium borohydride (1.74 mg) was added and the reaction mixturewas stirred at temperature 0-10° C. for 1-2 h. The progress of thereaction was monitored by TLC. The reaction mixture was quenched withacetic acid (0.2 mL), saturated solution of ammonium chloride (2 mL) andbrine (10 mL). The reaction mixture was extracted with ethyl acetate(3×15 mL). The combined organic layers were washed with brine, driedover anhydrous sodium sulfate, filtered, and evaporated in-vacuo to givecrude product 16 (46 mg). The crude product was used as such in the nextstep.

Preparation of (17)

A 50-mL, one-neck, round-bottomed flask equipped with a magneticstirrer, was charged with a solution of intermediate 16 in methanol andhydrochloric acid (a few drops). The reaction mixture was stirred atambient temperature for 1-2 h. The progress of the reaction wasmonitored by TLC. The reaction mixture was quenched with a solution ofsaturated sodium bicarbonate, then brine (10 mL) and extracted withethyl acetate (3×10 mL). The combined organic layers were washed withbrine (1×10 mL), and dried over anhydrous sodium sulfate (1 g),filtered, and the filtrate was evaporated in-vacuo to give crudeproduct. The crude product was purified by column chromatography using230-400 mesh silica gel and eluted with ethyl acetate in hexanes(10-70%). The fractions containing the desired product (lower spot onTLC) were evaporated in-vacuo to yield pure product 17 (22 mg, ˜50% overtwo steps, one isomer only).

Preparation of (18)

A 50-mL, one-neck, round-bottomed flask equipped with a magneticstirrer, was charged with a solution of intermediate 17 in methanol andthe solution of sodium hydroxide (15 mg in 1.0 mL of water). Thereaction mixture was stirred at ambient temperature overnight. Theprogress of the reaction was monitored by TLC. Additional amount ofsodium hydroxide (25 mg dissolved in 1.0 mL of water) was added andtemperature of the reaction mixture was raised to 45° C.-55° C. for 6-8h. The progress of the reaction was monitored by TLC. The solvent wasevaporated in-vacuo to remove methanol, and water was added to thereaction mixture. The aqueous layer was extracted with dichloromethane(3×10 mL) to remove impurities. The pH of the aqueous layer was adjustedto 2-3 by addition of dilute hydrochloric acid and the aqueous layer wasextracted with ethyl acetate (3×10 mL). The combined organic layers werewashed with water (1×10 mL), brine (1×10 mL), and dried over anhydroussodium sulfate (1 g), filtered, and the filtrate was evaporated in-vacuoto give crude product (314-d isomer of beraprost, 18 mg).

Preparation of (19)

A 50-mL, one-neck, round-bottomed flask equipped with a magneticstirrer, was charged with a solution of free 314-d isomer of beraprost(18) in methanol and the solution of sodium hydroxide (2 mg dissolved in1.0 mL of water). The reaction mixture was stirred at ambienttemperature for 1-2 h. The solvent was evaporated in-vacuo to removemethanol and water. Toluene (5 mL) was added to the residual, yellow,and viscous material and the toluene was removed in-vacuo to give thesolid sodium salt 314-d isomer of beraprost (21 mg). A chiral HPLC assayindicated 314-d isomer of beraprost (84%) and it was confirmed bycomparing with references of 314-d isomer of beraprost (one referenceconsists of 314-d isomer of beraprost and other reference consists ofmixture of four isomers including 314-d isomer of beraprost).

Example 2: Side-Chain Formation

Preparation of (21)

The benzyl-substituted oxazolidinone 20 was selected as the startingmaterial. It had given a high selectivity in the synthesis.Deprotonation of 20 with NaN(SiMe₃)₂ and treatment of the correspondingsodium enolate with freshly prepared 1-iodo-2-butyne, which was preparedfrom the commercially available 1-bromo-2-butyne, gave the substitutedoxazolidinone 21 in 70-90% yield. Reaction of oxazolidinone 21 with1-bromo-2-butyne never went to completion, even with excess of reagent.1-iodo-2-butyne can be prepared from 2-butyn-1-ol or 1-bromo-2-butyne,whereas the in-situ preparation of 1-iodo-2-butyne from 1-bromo-2-butyneis more convenient and preferable.

Preparation of (22)

To a 250 mL, three-necked, round-bottomed flask equipped with amechanical stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of oxazolidinone 21 (8.095 g) inEtOH (100 mL), followed by addition of Ti(OEt)4 (6.473). The mixture washeated to reflux for 7-10 h. The reaction mixture was concentrated in arotary evaporator at 20° C./50 mbar. The residue was dissolved in EtOAc(100 mL) and concentrated the rotary evaporator, and the crude materialwas adsorbed on silica gel and purified by column chromatography(gradient: ethyl acetate/hexanes, 2-6%) to give ester 22 (6.27 g).

Preparation of (23)

To a 250 mL, three-necked, round-bottomed flask equipped with amechanical stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of ester 22 (6.0 g) and[MeO(Me)NH₂]Cl (9.5 g) in THF (75 mL). To the solution was addeddrop-wise i-PrMgCl (48.6 mL, 2.0 M in THF) at 20° C. during 45 min by adropping funnel. After the mixture was stirred at 20° C. for 30 min,aqueous NH₄Cl (4 mL) was added. The mixture was allowed to warm toambient temperature and diluted with MTBE (25 mL). The suspension wasfiltered through a pad of Celite and concentrated in vacuo. The crudeproduct was purified by column chromatography (gradient: EtOAc/hexanes,5-25%) to afford Weinreb amide 23 (3.45 g, 73% over two steps) as acolorless oil.

Preparation of (24)

To a 250 mL, three-necked, round-bottomed flask equipped with amechanical stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of Dimethyl methylphosphonate (5.279g) in THF (30 mL), followed by drop-wise addition of n-BuLi (22.16 mL of1.6 M in hexanes) at 78° C. by a dropping funnel. The mixture wasstirred at 78° C. for 1 h and then a solution of amide 23 (3.00 g) inTHF (20 mL) was added during 30-45 minutes via the dropping funnel.After the mixture was stirred at 78° C. for 2 h, aqueous NH₄Cl (4 mL)was added. The reaction mixture was allowed to warm to ambienttemperature, diluted with MTBE (50 mL), filtered and concentrated invacuo. The crude product was purification by column chromatography(gradient, EtOAc/hexanes, 0-8%) to afford phosphonate 24 (3.799 g, 92%).

Example 3: Preparation of Enone Intermediate from Ester Diol

Step 1: Protection of the Primary Alcohol

A 500 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution ofester diol (1) (10.00 g) in dichloromethane (200 mL). To this solutiontriethylamine (13.21 g), 4-(dimethylamino)pyridine (4.0 g), and DMF (20mL) were added at ambient temperature under argon. The mixture wasstirred until a clear solution was obtained. The reaction was stirredfor ˜31 h at ambient temperature. After ˜31 h, the progress of thereaction was monitored by TLC. The mixture was washed with saturatedammonium chloride (200 mL). The organic layer was separated, dried overanhydrous sodium sulfate, filtered, and concentrated in vacuo to givethe crude product (2) as a viscous oil. The crude product from another10-g batch was combined and purified by column chromatography using230-400 mesh silica gel and eluted with a gradient solvent of ethylacetate in hexanes (5-50%). The fractions containing the desiredcompound (by TLC) were evaporated in vacuo to yield trityl ether (2)(33.82 g, 94.6% from two 10-g batches). The compound was characterizedby spectral data.

Step 2: Protection of the Secondary Alcohol

A 1000 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution oftrityl ether (2) (39.50 g) in anhydrous dichloromethane (600 mL). Tothis solution, 2,6-lutidine (18.51 g) was added at ambient temperatureunder argon. The mixture was stirred until a clear solution wasobtained. The mixture was cooled to −15° C. and TBDMS triflate (22.84 g)was added in portions while maintaining the temperature below −10° C.The reaction was stirred for ˜1 h and the progress of the reaction wasmonitored by TLC. At this stage the reaction was complete. To thereaction mixture hexanes were added (600 mL) and temperature was allowedto rise to ambient. This mixture was passed through a pad of 230-400mesh silica gel (384 g) and eluted with a gradient solvent of ethylacetate in hexanes (5-15%). The fractions containing the desiredcompound were evaporated in vacuo to yield silyl ether (3) (47.70 g,99.6%). The compound was characterized by spectral data.

Step 3: Deprotection of the Primary Alcohol

A 500 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution oftrityloxy-TBDMS ether (3) (14.58 g) in anhydrous dichloromethane (175mL). To this solution, diethylaluminum chloride (22.00 mL, 1M indichloromethane, 1.0 eq.) was added at ambient temperature under argon.The reaction was stirred for −3 h and the progress of the reaction wasmonitored by TLC. At this stage reaction was not complete and an extraone equivalent of diethylaluminum chloride (22.00 L, 1M indichloromethane, 1.0 eq.) was added at ambient temperature, and thereaction mixture was stirred for another 3 h while the progress wasmonitored by TLC. After a total of 6 h the reaction mixture showed thepresence of some starting material and another 0.5 equivalent of diethylaluminum chloride (11.00 mL, 1M in heptane, 0.5 eq.) was added atambient temperature and reaction mixture was stirred for another 1 h andprogress of the reaction was monitored by TLC. At this stage reactionwas complete, and the reaction mixture was cooled to 0° C. To thereaction mixture, saturated sodium bicarbonate solution (240 mL) wasadded (Note 2). Once the temperature raised to ambient, and the compoundwas extracted with dichloromethane. The combined extracts ofdichloromethane were washed with brine, dried over sodium sulfate andevaporated in vacuo to obtain a crude, viscous oil (14.01 g). This crudecompound was passed through a pad of 230-400 mesh silica gel (197 g) andeluted with a gradient solvent mixture of ethyl acetate in hexanes(10-50%). The fractions containing the desired compound were evaporatedin vacuo to yield hydroxy-silyl ether (4) (8.54 g, 92.3%). The compoundwas characterized by spectral data.

Step 4: Oxidation of Primary Alcohol and Coupling Resulting in EnoneIntermediate

To a cooled (−78° C.) and stirred solution of oxalyl chloride (23.00 mL)in dichloromethane (60 mL) was added slowly a solution of dimethylsulfoxide (4.33 mL) in dichloromethane (35 mL) under argon. Afterstirring for 45 minutes at −78° C. to −70° C., a solution of alcohol (4)(8.54 g) in dichloromethane (60 mL) was added to this reaction mixturewhile maintaining the temperature below −65° C. After stirring for 60minutes at −65° C., temperature of reaction mixture was raised to −45°C. to −40° C. and stirred for 60 minutes at this temperature. Thisreaction mixture was cooled to −65° C. and quenched by slow addition oftriethylamine (14.15 mL) (Note 1). The reaction mixture was stirred foranother 30 minutes at −65° C. and the completion of reaction was checkedby the TLC. The temperature of reaction mixture was raised to ambientand water (60 mL) was added. The two-phase mixture was stirred for 5minutes at room temperature after which the organic phase was separatedand the aqueous phase was extracted with dichloromethane (2×75 mL) toensure complete extraction of product into the organic layer. Thecombined organic extracts were washed with brine (100 mL), dried oversodium sulfate and evaporated in vacuo to obtain crude aldehyde (9.77g). In a separate 500-mL, two-necked, round-bottom flask equipped with amagnetic stir bar and an argon inlet-outlet adapter, a solution ofphosphonate side chain (8.50 g) in MTBE (175 mL) was charged. To thisLiOH.H2O (1.86 g) was added and the mixture was stirred for −1 h. After−1 h, a solution of crude aldehyde (5) in MTBE (175 mL) was added slowlyover a period of 10 minutes and stirred until completion of reaction(Note 3). Progress of reaction was monitored by TLC (Note 3). After thereaction was complete, the reaction mixture was quenched by adding water(175 mL) and the mixture stirred for 15 minutes. The organic layer wasseparated and aqueous layer was extracted with ethyl acetate (3×70 mL).The combined organic extracts were washed with water (70 mL), brine (30mL), dried over sodium sulfate and evaporated in vacuo to obtain acrude, viscous liquid of enone intermediate (6) (11.22 g). This crudeenone intermediate (6) was passed through a pad of 230-400 mesh silicagel (328 g) and eluted with a gradient solvent of ethyl acetate inhexanes (2-20%). The fractions containing the desired compound wereevaporated in vacuo to yield enone (6) (19.42 g, 80%; This crudecompound was combined with 14.99 g of crude compound from another lotand a combined column chromatography was performed on two lots). Thepure compound was characterized by spectral data.

Example 4: Preparation of Compound (A)

Option 1: Reduction/Deprotection

Step 1: Selective Reduction

A 100 mL, three-necked, round-bottom flask equipped with a magnetic stirbar, a thermocouple, and an argon inlet-outlet adapter was charged withenone compound (0.11 g) and anhydrous toluene (5.0 mL). A solution of(R)-(+)-2-methyl CBS oxazaborolidine (1.0 M in toluene) (0.43 mL) wasadded under argon at ambient temperature. The mixture was cooled to ˜0°C. (dry ice/acetone-bath), and borane-methyl sulfide complex (0.32 mL)was added slowly maintaining the temperature between −40° C. and −30° C.After complete addition, the reaction mixture was stirred for 1-2 h at−30° C. to −25° C. The progress of the reaction was monitored by TLC.The reaction mixture was carefully quenched by slow addition of methanol(2.0 mL) over a period of 2-3 minute maintaining the temperature between−15° C. and −10° C. The reaction mixture was allowed to warm to roomtemperature and the stirring was continued for another 20-30 minutes. Atthis stage, saturated aqueous ammonium chloride solution (5.0 ml) wasadded with stirring. The organic layer was separated, and the aqueouslayer was extracted with ethyl acetate (2×15 mL). The combined organiclayers were washed with brine (10 mL), dried over anhydrous sodiumsulfate, filtered and concentrated in vacuo to give crude alcohol (A)(0.27 g). This crude alcohol (A) was passed through a pad of 230-400mesh silica gel (22.5 g) and eluted with a gradient solvent of ethylacetate in hexanes (0-12%). The fractions containing the desiredcompound were evaporated in vacuo to yield pure alcohol (7) (0.096 g,87.2%). The compound was characterized by spectral data.

Step 2: Deprotection of Protected Alcohol

To a solution of TBDMS protected ether (2.67 g) in methanol (50 mL) wasadded 10% aqueous HCl 10.00 mL) at room temperature. The reactionmixture was stirred at ambient temperature until completion of reaction.After −1 h the reaction mixture was checked by TLC for its completion.At this stage, the reaction mixture was neutralized with saturatedsodium bicarbonate 10 mL) to pH 7-8 and concentrated in vacuo to removemethanol. The reaction mixture was diluted with water 10 mL) and themixture was then extracted with ethyl acetate (3×30 mL). The combinedethyl acetate extracts were washed with brine (15 mL), dried (Na₂SO₄),filtered and concentrated in vacuo to give beraprost ester (A) as acrude, pale-yellow, viscous liquid (2.31 g). The crude product waspurified by column chromatography using a gradient solvent of ethylacetate in hexanes (0-90%). The fractions containing the desiredcompound were evaporated in vacuo to yield beraprost ester (A) (1.26 g)which was crystallized using a ethyl acetate and cyclopentane mixture toobtain ester with a chiral purity of 96.24% (by HPLC); mp 82-83° C.(dec.); Required: C=72.79; H=7.82; Found C=72.86; H=7.41. The compoundwas characterized by spectral data.

Option 2: Deprotection/Reduction

Step 1: Deprotection of Protected Alcohol

To a solution of enone (0.450 g) in methanol (10 mL) was added 10%aqueous HCl (0.90 mL) at ambient temperature. The reaction mixture wasstirred at ambient temperature until completion of reaction. After −3 hthe reaction mixture was checked by TLC for its completion. At thisstage, the reaction mixture was neutralized with saturated sodiumbicarbonate to pH 7-8 and concentrated in vacuo to remove methanol. Thereaction mass was diluted with water (10 mL) and the mixture wasextracted with ethyl acetate (2×15 mL). The combined ethyl acetateextracts were washed with brine (10 mL), dried (Na₂SO₄), filtered andconcentrated in vacuo to give the keto alcohol as a crude, pale-yellow,viscous liquid (0.400 g). The crude product was crystallized using aethyl acetate and hexanes mixture to obtain pure, crystallineketo-alcohol (0.210 g, 60%); mp 75-76° C.; The compound wascharacterized by spectral data.

Step 2: Selective Reduction

A 100 mL, three-necked, round-bottom flask equipped with a magnetic stirbar, a thermocouple, and an argon inlet-outlet adapter was charged withketo-alcohol (8) (3.25 g) and anhydrous toluene (100 mL). A solution of(R)-(+)-2-butyl CBS oxazaborolidine (1.0 M in toluene) (23.8 mL) wasadded under argon at room temperature. The mixture was cooled to −15° C.(dry ice/acetone-bath), and catecholborane (23.8 mL) was added slowlymaintaining the temperature between −15° C. and −10° C. After completeaddition, the reaction mixture was stirred for 1-2 h while slowlyallowing the temperature to raise to ambient temperature. The progressof the reaction was monitored by TLC. The reaction mixture was carefullyquenched by slow addition of methanol (50 mL) over a period of 10minutes maintaining the temperature between −15° C. and −10° C. Thereaction mixture was allowed to warm to room temperature and thestirring was continued for another 20-30 minutes. At this stage,saturated aqueous ammonium chloride solution (10 ml) was added withstirring. The organic layer was separated, and the aqueous layer wasextracted with ethyl acetate (3×50 mL). The combined organic layers werewashed with brine (15 mL), dried over anhydrous sodium sulfate, filteredand concentrated in vacuo to give crude beraprost ester (A). The crudeproduct was purified by column chromatography using a gradient solventof ethyl acetate in hexanes (0-90%). The fractions containing thedesired compound were evaporated in vacuo to yield beraprost ester (A)(2.53 g, 77%). A small sample was crystallized using an ethyl acetateand hexanes mixture to obtain analytically pure beraprost ester diol mp75-76° C. The compound was characterized by spectral data.

Example 5: Compound A to Beraprost 314d to a Salt

Synthesis of Beraprost 314d

To a solution of beraprost ester (A) (0.700 g) in methanol (10 mL) wasadded a solution of sodium hydroxide (0.815 g in 2.0 mL water) at roomtemperature. The reaction mixture was stirred at room temperature for−16 h and the progress of the reaction was monitored by TLC. Thereaction mixture was concentrated in vacuo to remove methanol anddiluted with water (10 mL). This mixture was acidified with 10%hydrochloric acid solution to pH 2-3. The mixture was extracted withethyl acetate (2×10 mL). The combined ethyl acetate extracts were washedwith brine (1×10 mL), dried (Na₂SO₄), filtered and concentrated in vacuoto give the desired stereoisomer of beraprost (314d) as foamy solid(0.700 g). This acid was used out as such for potassium salt formation

Synthesis of Potassium Salt of Beraprost (314d)

A 100-mL, two-necked, round-bottom flask equipped with a magneticstirrer and a thermometer was charged with beraprost (314d) (0.500 g)and ethyl acetate (15 mL). This mixture was warmed to 75-80° C. toobtain a clear solution. To this clear solution, potassium hydroxide(0.066 g) in ethanol (3.0 mL) was added and stirred for few minutes at75-80° C., then the mixture was allowed to cool to ambient temperatureover a period of approximately 2 h. At ambient temperature, theprecipitated product was isolated by filtration and washed with ethanol.The product was transferred from Buchner funnel to a glass dish forair-drying overnight in a fume hood to yield free flowing white-solidsalt of beraprost (0.420 g); the solid was crystallized from ethanol andwater to obtain pure stereoisomer of beraprost potassium salt, chiralpurity 99.6% by Chiral HPLC; mp 270-272° C. (dec.); Required: C=66.03;H=6.70; Found C=65.82; H=6.67. The compound was characterized byspectral data.

Example 6: Synthesis of Side Chain with Chiral Methyl

Step 1:

A 2-L, three-necked, round-bottom flask equipped with a mechanicalstirrer and an argon inlet-outlet adapter connected to a bubbler wascharged with a solution of (R)-(+)-4-(diphenylmethyl)2-oxazolidinone (2,25 g in 200 mL of THF). The solution was cooled to −78° C. under argon.To the solution was added n-butyllithium in hexanes (1.6 M, 64.80 mL)drop wise at −78° C. over a period of 45-60 minutes. The reactionmixture was stirred at −78° C. for 30-45 min. Then, propionyl chloride(20.10 g dissolved in 30-50 mL of dry THF) was added drop wise at −78°C. over 15-30 min. The mixture was stirred at −78° C. for 1-2 h (Note1). The reaction mixture was quenched with saturated solution ofammonium chloride (15 mL) at −78° C. to −60° C. and then allowed towarm-up to ambient temperature. An additional amount of ammoniumchloride (100 mL) was added to the reaction mixture at ambienttemperature and the mixture was swirled in separatory funnel. Theorganic layer was separated from aqueous layer. The aqueous phase wasextracted with MTBE (2×100 mL). The combined organic phases were washedwith aqueous NaHCO₃ (100 mL), brine (100 mL), then dried over anhydrousNa₂SO₄ followed by filtration. The filtrate was concentrated in vacuo toafford crude solid product (30.38 g, quantitative).

Step 2:

A 500-mL, round-bottom flask equipped with a magnetic stirrer and anargon inlet-outlet adapter connected to a bubbler was charged with1-bromo-2-butyne (23.21 g) and THF (100-120 mL) under argon at roomtemperature. To the solution of 1-bromo-2-butyne, sodium iodide (27.90g) was added. The reaction mixture was stirred for 2-3 h at ambienttemperature. The suspension was filtered using a Whatmann filter paperNo. 50 and the solid washed with dry THF (15-30 mL). The filtratecontaining 1-iodo-2-butyne in THF was used in the next step.

Step 3:

A 2-L, three-necked, round-bottom flask equipped with a mechanicalstirrer and an argon inlet-outlet adapter connected to a bubbler wascharged with a solution of NaN(SiMe₃)₂ (1.0 M, 174 mL). To this solutionwas added a solution of oxazolidinone (36 gin 50-80 mL of THF) drop wiseat −78° C. After the mixture was stirred at −78° C. for 60-120 min,1-iodo-2-butyne (freshly prepared in THF in step one) was added dropwise at −78° C. over a period of 45-60 min using a dropping funnel. Themixture was stirred for 2 h, and then quenched the reaction mixture withacetic acid (11 mL) at −78° C. The mixture was allowed to warm toambient temperature and aqueous sodium chloride (500-750 mL) was added.The organic layer was separated from the aqueous layer. The aqueousphase was extracted with MTBE (3×400 mL). The combined organic phaseswere washed with aqueous NaHCO₃ (100 mL), then dried over anhydrousNa₂SO₄, followed by filtration. The filtrate was concentrated in vacuoto ⅕th of the total volume. Ethanol (150 mL) was added and the mixtureconcentrated in vacuo to a slurry. An additional amount of ethanol (200mL) was added and then concentrated again in vacuo to a slurry in orderto remove other solvents carried over from reaction and work-up.

Crystallization: To the resulting slurry, ethanol 300-350 mL was addedand mixture was heated to obtain a clear solution. The clear solutionwas allowed to cool slowly to ambient temperature. The resulting solidwas collected by filtration and washed with a solution of ethanol inhexanes (50%, 50-150 mL). The solid product was transferred to glasstray and air-dried to afford white, crystalline oxazolidinone (24.74 g,59%), mp 128-130° C.

Example 7: Synthesis of Phosphonate Side Chain

Step 1:

A 500-mL, round-bottom flask equipped with a mechanical stirrer wascharged with a solution of oxazolidinone 8 (24.50 g) in THF (295 mL),water (114 mL) and LiOH (2.273 g). The mixture was stirred at ambienttemperature for 16-24 h. A saturated solution of sodium bicarbonate(50-75 mL) was added to the reaction mixture slowly while stirring. Thereaction mixture was extracted with MTBE (5×100 mL) to remove the chiralauxiliary and impurities. The aqueous layer was adjusted to pH 3-4 byaddition of dilute hydrochloric acid and extracted with MTBE (3×150 mL).The combined organic layers were washed with brine (1×150 mL), and thendried over anhydrous Na₂SO₄, followed by filtration. The filtrate wasconcentrated in vacuo to give crude carboxylic acid (6.4 g, 74.5%).

Step 2:

A 500-mL, round-bottom flask equipped with a magnetic stirrer wascharged with carboxylic acid (10) (6.35 g),2-chloro-4,6-dimethoxy-1,3,5-triazine (11.93 g), and N-methylmorpholine(14.6 mL) in THF (70-100 mL). The suspension was stirred at ambienttemperature for 1-2 h. After stirring for 1-2 h, MeO(Me)NH.HCl (5.89 g)was added and the mixture stirred at RT overnight (16-18 h). To thereaction mixture, hexane (50-100 mL) was added. The slurry was filteredthrough a pad of Celite. The Celite bed was washed with hexanes (50-100mL). The filtrate was concentrated in vacuo to afford crude amide (11).The crude product was dissolved in hexane (50-100 mL) and filtered againthrough a pad of Celite in order to remove suspended solid impurities.The Celite bed was washed with hexanes (50-100 mL). The filtrate wasconcentrated in vacuo to afford crude product. The crude product waspurified by silica gel column chromatography (gradient: EtOAc/hexanes,5-25%) to afford Weinreb amide (7.2 g, 85%) as a colorless oil with a98.42% purity (by chiral HPLC).

Step 3:

A 500-mL, three-necked, round-bottom flask equipped with a magneticstirrer and an argon inlet-outlet adapter connected to a bubbler wascharged with a solution of dimethyl methylphosphonate (A) (13.00 g) inTHF (50 mL) followed by drop wise addition of n-BuLi (1.6 M in hexanes,52.50 mL) at −78° C. using a dropping funnel. The mixture was stirred at−78° C. for 1 h and then a solution of amide 11 (7.10 g) in THF (20-30mL) was added over a period of 30-45 minutes using a dropping funnel.After complete addition, the mixture was stirred at −78° C. for 2 h,then the reaction was quenched with aqueous NH₄Cl (100 mL). The mixturewas allowed to warm-up to ambient temperature. The mixture was extractedwith ethyl acetate (3×75 mL). The combined organic layers were washedwith brine (1×50 mL), then dried over anhydrous Na₂SO₄, followed by thefiltration. The filtrate was concentrated in vacuo to afford crudeproduct. The crude product was purified by column chromatography(gradient, EtOAc/hexanes, 10-100%) to afford(S)-3-methyl-2-oxohept-5-ynylphosphonic acid dimethyl ester (9.218 g,95%).

All of the publications, patent applications and patents cited in thisspecification are incorporated herein by reference in their entirety.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the present invention is not so limited. It willoccur to those of ordinary skill in the art that various modificationsmay be made to the disclosed embodiments and that such modifications areintended to be within the scope of the present invention.

What is claimed is:
 1. A potassium salt of a beraprost stereoisomerhaving the following formula:

wherein the beraprost stereoisomer has an isomeric purity of at least90%.
 2. The potassium salt of claim 1, wherein the beraproststereoisomer has an isomeric purity of at least 95%.
 3. The potassiumsalt of claim 1, wherein the beraprost stereoisomer has an isomericpurity of at least 98%.
 4. The potassium salt of claim 1, wherein theberaprost stereoisomer has an isomeric purity of at least 99%.
 5. Thepotassium salt of claim 1, wherein the beraprost stereoisomer has anisomeric purity of more than 99%.
 6. A method of treating pulmonaryhypertension, comprising administering to a subject in need thereof apotassium salt of a beraprost stereoisomer having the following formula:

wherein the beraprost stereoisomer has an isomeric purity of at least90%.
 7. The method of claim 6, wherein the beraprost stereoisomer has anisomeric purity of at least 95%.
 8. The method of claim 6, wherein theberaprost stereoisomer has an isomeric purity of at least 98%.
 9. Themethod of claim 6, wherein the beraprost stereoisomer has an isomericpurity of at least 99%.
 10. The method of claim 6, wherein the beraproststereoisomer has an isomeric purity of more than 99%.